1. Field of the Invention
The present invention relates in general to an NC (Numerical Control) machine tool numerical controller and numerical control method, and in particular, to a numerical controller and a numerical control method for numerical control machine tools performing an orbit control.
2. Description of the Related Art
Recent years have observed the development (Japanese Patent No-3093935) of a turning operation method as a turning operation method for NC machine tools, in which a boring bat (tool) mounted on a spindle is controlled to always be oriented in a radial direction (normal direction) of circular arc by the synchronization of a circular interpolatory movement of a center of the spindle on a plane perpendicular to the spindle and a rotational movement of the spindle, to execute a boring process. This turning operation method, called orbit boring from the mode of movement, is advantageous in that the boring of an arbitrary hole size can be performed with a single boring bar.
The NC machine has controlled axes, which have their maximum feed speeds and maximum accelerations factory-set to be adequate. Disclosed techniques (Japanese Patent Application Laying-Open Publication No. 4-245505) teach limiting the feed speed of controlled axis within a prametrically set maximum feed speed.
As orbit boring takes a radial movement as a cut-in or escape action during operation, with a resultant combination between a feed speed of circular interpolatory movement (as an orbital motion speed) and a feed speed for the cut-in or escape action (as a radial spend), if the orbital motion speed exceeds a certain given value, an associated axis may undergo excessive feed speed or acceleration over a factory-set upper limit.
Controlled axis with an excessive feed speed or acceleration over a factory-set upper limit may suffer from, for example, a torque saturation phenomenon with a resultant lost of control, or an excessive error over a permissible value with a failure to perform a conforming process within a permissible range of precision.
The issue described likely appears not simply in the orbit boring, but also in a contour processing by ordinary circular interpolation, when the feed speed of controlled axis is increased for high-speed operation, with a failure to perform a conforming process within a permissible range of precision required therefore.
The present invention has been made to solve problems described. It therefore is an object of the present invention to provide a numerical controller and a numerical control method for NC machine tools adapted, in a control that accompanies a circular interpolation, such as in an orbit boring, even when making a radial motion to take a cut-in or escape action, so that feed velocity or acceleration of controlled axis is kept from exceeding a factory-set maximum feed velocity or acceleration, ensuring a conforming process to be performed within a permissible range of precision.
To achieve the object, an aspect of the invention provides a numerical control method for NC machine tools to perform a contour describing control, comprising: calculating a permissible range of a physical index representing one of a velocity and an acceleration of a tool; and controlling the physical index within the permissible range.
Further, to achieve the object, another aspect of the invention provides a numerical controller for NC machine tools to perform a contour describing control, comprising: a calculator for calculating a permissible range of a physical index representing one of a velocity and an acceleration of a tool; and a controller for controlling the physical index within the permissible range.